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Phosphate & dead leaves

>Date: Sun, 30 Mar 1997 17:17:18 -0500 (EST)
>From: Ellistonk at aol_com
>Subject: Phosphate & dead leaves
>> I've seen people on the APD list in the past recommend plant sticks
>> with phosphate. They reason that as long as the phosphate remains in
>> the gravel, that they will hopefully avoid the algae problems caused
>> by excessive phosphates in the water column. 
>> It seems to me that the plants will absorb the phosphates in the
>> substrate and grow. Eventually plant leaves will fall off and begin
>> decomposing and release phosphates now into the water column. I would
>> also guess that that same thing would happen if I did _not_ use these
>> plant sticks, but the phosphates would be released at a lower level.
>My first thought when I read this was, "I vacuum/pick out dead leaves before
>they decompose, so I wouldn't have to worry about this". Then I remembered
>something I read once regarding ponds & leaves, and now have the following
>question. What I read was that when a leaf falls into a pond, most of the
>phosphate is leached out into the water within about 10-15 minutes or so.
>Vacuuming out dead leaves after that wouldn't reduce phosphate levels much.
>So, does anyone know approximately when most of the phosphate leaches out of
>a dead or dying leaf of a submerged plant in our tanks? Just how dead does it
>have to be? If I were worried about excess phosphate, should I prick out the
>dying leaves at the first sign of yellowing? Or is it already too late at
>that point?

As long as the leaf is attached, I believe that the phosphate recycles from
the old leaves into the other parts of the plant. I have never actually seen
this, just what I have read <g>. The same is true for N and K and someother
stuff.Now, if the leaf falls off, as during pruning, the dead leaf WILL
release its P and other nutrients back into the environment. 

I usually don't prune the old leaves. First, because I don't usually see any
<g> - lots and lots of plants, and as I am getting older, so are my eyes
<g>, but also because it is useful to see if the outer leaves are getting
holes. This can tell you that the new leaves need more nutrients and are
recyling them from the older part of the plant. Some of this is OK, but when
it is occuring too much it means that there is a shortage of something...
like N.

Neil Frank      Aquatic Gardeners Association         Raleigh, NC
      The Aquatic Gardener - journal of the AGA -  now in its seventh year!!